Method of preparing void free fibers from acrylonitrile polymers



April 7, 1965 ,P. KNUDSEN ETAL 3,180,845

ING D F METHOD 0 REPAR REE FIBERS FROM A R LONITR POLYMERS led Oct. 20,1961 I/VVE/V TORS JOHN R KNUDSE/V HOWARD 6. (JAR/(El BYQZQu/K ATTORNEYUnited States Patent 3,180,845 METHGD OF PREPARlNG V011) FREE FlBERSFRQM ACRYLONITRHLE PULYMERS John P. Knudsen, Raleigh, and Howard G.Clarir Ill, Chapel Hill, Natl, assignors, by mesne assignments, toMonsanto Company, a corporation of Delaware Filed Get. 20, 1961, Ser.No. 146,555 13 Claims. (Cl. ass-see This invention relates to thepreparation of improved fibers from acrylonitrile polymers throughcontrol of the coagulation properties of spinning solutions of thesepolymers. More particularly, this invention relates to the use ofcertain easily soluble alkylene glycol polymers compatible in solutionwith polyacrylonitrile to control the formation of internal voids in thefibers during coagulation. Certain acrylonitrile polymers, copolymers,and polymer blends containing at least 80% acrylonitrile commonly usedfor the preparation of synthetic fibers by wet spinning yield fiberscontaining large numbers of internal voids when solutions of thesepolymers in organic solvents are coagulated in aqueous spin bathsparticularly at high spinning speeds. These voids appear to form at theinstant of coagulation due to rapid skin formation and inward diffusionof spin bath liquors. Voids so formed persist in the fiber throughoutits further processing and contribute undesirable properties such aspoor abrasion resistance and reduced luster to the finished fiber.

Accordingly, it is the object of this invention to provide spinningsolutions of acrylonitrile polymers which can be readily coagulated togive substantially void free fibers with improved luster and abrasionresistance. A further object of this invention is to provide a methodfor spinning high quality acrylonitrile fibers at increased spinningspeeds. Other objects and advantages will become apparent from thedescription of the invention which follows hereinafter.

In general, these and other objects of the invention are accomplished byincorporating into the spinning solution a suitable small quantity of apolymer which is both compatible with the acrylonitrile polymer and alsosoluble or highly swellable by the coagulation medium employed.Typically, these conditions are met by incorporating in the spinningsolution a suitable amount of polyethylene glycol, polypropylene glycolor polybutylene glycol. The solution may then be wet spun into a.coagulation bath according to the usual well known methods, and willresult in fibers of improved characteristics,

The mode of addition of the polyglycol is unimportant. That is thepolyglycol may be blended with the acrylonitrile polymer duringpreparation of the spinning solution by any convenient means. Thepolymers may be dissolved sequentially in either order, or the two maybe dissolved separately and the solutions mixed. However, both polymerand polyglycol must be completely and uniformly dispersed throughout thesolution on order to ensure proper performance of the invention. Thepolymerpolyglycol solution is then extruded into a coagulation bath. Theimproved character of acrylonitnile fibers produced in this manner isevident by an examination of the accompanying drawings.

In the drawings,

FIGURE 1a shows a drawing of a mricrophotograph cross-section view ofpolyacrylonitrile fibers spun with 2.5% polyethylene glycol of 1,000molecular weight in the spinning solution and subjected to a jet stretchof 1.04. Jet stretch is the rate of filament take-up divided by theextrusion rate. FIGURE 1 shows polyacrylonitrile fibers spun withoutpolyethylene glycol and subjected to the tear shaped areas whichcharacteristically form while the filament is coagulating, is greatlyreduced in FIGURE la using polyethylene glycol. FIGURES 2a and 2 comparepolyacrylonitrile fibers spun with 2.5% polyethylene glycol of 1,000molecular weight in the spinning solution and none respectively, towhich a 2.01 jet stretch has been applied. FIGURES 3a and 3 showpolyacrylonitrile fibers prepared with 2.5% polyethylene glycol of 1,000molecular weight in the spinning solution and none respectively, towhich a 3.10 jet stretch was applied. In all three comparisons thereduction of voids when polyethylene glycol is present in the spinningsolution is clearly evident. A reduced occurrence of voids improves theabrasion resistance and other desirable qualities.

The polyglycols of this invention may be employed in an amount of fromabout 2 to 25 percent of the polymer by weight. The molecular weight ofthese polyglycols may vary from about 400 to 4,000, preferably around600 to 2,000.

Any organic polyacrylonitrile solvent which does not undergo sidereactions with the polyglcols of this invention can be used in thepractice of this invention. Among the preferable solvents areN,N-dimethylacetamide, dimethylsulfoxide, ethylene carbonate, and thelike.

The use of polyethylene glycol, polypropylene glycol or polybutyleneglycol in accordance with the present invention, effects improvements inproperties of fiber spun from all suitable solutions of acrylonitrilepolymers. The invention is applicable not only topolyacrylonitrlle butalso to copolymers, interpolymers, and blends thereof, particularlythose containing at least 80 percent by weight of polymerized orcopolyrnerized acrylonitrile. Such polymeric materials includeacrylonitrile fiber forming polymers with readily dyeable basiccopolyrners, the blend having an overall polymerized acrylonitrilecontent of at least 80 percent by weight.

For example, the polymer may be a copolymer of 80 to 98 percent ofacrylonitrile and from 2 to 20 percent of another copolymerizablemonoolefinic monomer. Suitable copolymerizable mono-olefinic monomersinclude acrylic, alpha-chloroacrylic and methacrylic acids; the

acrylates, such as methylmethacrylate, ethylmethacrylate,

butylmethacrylate, methoxymethyl methacrylate, betaa jet stretchof.l.04. A comparison of FIGURE la and FIGURE 1 clearly shows that theoccurrence of voids,

chloroethyl methacrylate, and the corresponding esters of acrylic andalpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinylbromide, vinylidene chloride, l-chloro-lbromoethylene,methacrylonitrile, acrylamide and methacrylarnide,alpha-chloroacrylamide, or monoalkyl substitution products thereof;methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinylchloroacetate, vinyl propionate and vinyl stearate; N-vinylimides, suchas N-vinylphthalirnide and N-vinylsuccinimide; methylene malonic esters,itaconic acid and itaconicester; N-vinylcarbazole; vinylfuran; alkylvinyl esters; vinyl sulfonic acid, ethylene alpha, beta-dicarboxylicacids or their anhydrides or derivatives, such as diethylcitraconate,diethyh' mesaconate; styrene, vinyl naphthalene; vinyl-substitutedtertiary heterocyclic amines such as the vinyl pyridines andalkyl-substituted vinylpyridines for example, 2-vinylpyridine,4-vinylpyrid=ine, Z-methyl-S-vinylpyridine and to l8 percent of anothercopolynier'izable mono-olefinic substance, such as methacrylonitrile,vinyl acetate, methyl methacrylate, vinyl chloride, vinylidene and thelike.

The polymer can also be a blend of polyacrylonitrile or a copolymer offrom 80 to 98 percent acrylonitrile and from 1 to 20 percent of at leastone other mono-olefinic copolymerizable monomeric substance with from 2to 50 percent of the weight of the blend of a copolymer of from 30 to 90percent of a vinyl-substituted tertiary heterocyclic amine and from to70 percent of at least one other mono-olefinic copolymerizable monomerpreferl0 ably, when the polymeric material comprises a blend, it will bea blend of from 80 to 99 percent of a copolyrner of 80 to 98 percentacrylonitrile and from 2 to 20 percent of another mono-olefinic monomer,such as vinyl acetate, which is not receptive to dye stuff, with from 1to percent of a copolymer of from 30 to 90 percent of avinyl-substituted tertiary heterocyclic amine such as vinylpyridine, al-vinylimidazole, or a vinyl lactam, and from 10 to 70 percent ofacrylonitrile to give a dyeable blend having an overallvinyl-substituted tertiary 0 heterocyclic amine content of from 2 to 10percent based on the weight of the blend.

While the preferred polymers employed in the instant invention are thosecontaining at least 80 percent acrylonitrile, generally recognized asthe fiber-forming acrylonitrile polymers, it will be understood that theinvention is likewise applicable to polymers containing less than 80percent of acrylonitrile when such polymers are useful in formingfibers.

The polymers useful in the practice of the present invention may beprepared by any conventional polymerization procedures, such as masspolymerization methods, solution polymerization methods or aqueousemulsion procedures. If it is desired to produce shaped articles fromthe acrylonitrile polymer solutions of the present invenlow. Thefibrillation measurement is comparative and such measurement is made ona fabric formed from the fibers. The degree of fibrillation isdetermined on a tricot knit tape and the value obtained is called atricot rating or TR. The tape is flex abraded for 150 cycles on a Strollabrader or Universal wear tester using the flexing bar with a 2 lb.tenison and /2 lb. weight on the head. Two such abrasions are made oneach tape while dry and then EXAMPLE II To further define thelimitations and utility of the invention a series of polymer solutionswere prepared in N,N-dimethylacetamide containing 25% of theacrylonitrile polymers used in Example I and 2.5% of polyethylene glycolof varying molecular weights and spun under constant conditions intocoagulating baths containing 55% N,N-dimethylacetamide and water at 55C. The resulting fibers were characterized by counting the averagenumber of voids in a 10 micron length of unoriented fiber as well as bythe tensile and abrasion tests described in Example I. The results areshown in Table II below.

tion which have a modified appearance or modified properties, variousagents may be added to the solutions to accomplish these effects eitherprior or after the addition of one of the polyglycols of this inventionthereto without any ill effects thereon. Such added agents might bepigments, dyes, anti-static agents, fire-retarding agents, and the like.Solutions containing from 8 to 30 percent by weight of acrylonitrilepolymers may be employed, with the preferred concentration range beingfrom 15 to 25 percent.

The invention is further illustrated by the following examples showingthe improvements obtained by adding polyethylene glycol to acrylonitrilepolymer solutions. In the examples all parts and percents are by weight.

EXAMPLE I This example involves preparing a spinning dope in the normalfashion to which polyethylene glycol (PEG) has been added. A solutionwas prepared by mixing 25 percent of an acrylonitrile copolyrnercontaining 93.7 percent acrylonitrile and 6.3 percent vinyl acetate and2.5 percent of PEG having an average molecular Weight of 7 0 1,000 withN,N-dimethylacetamide and stirring at about 50 C. until a solution wasformed. The solution was then spun to fiber according to normal wetspinning processes. Typical tensile properties of fibers spun from thissolution and the corresponding control are tabulated be- These resultsclearly indicate a region of maximum efficacy in the range of 4004,000molecular weight for the PEG additive. They show the reduction in voidnumber and improvement in abrasion character which marks the presentinvention. They also suggest the unsuitability of polymersincompatibility with the acrylonitrile polymer for the presentinvention.

EXAMPLE III To further establish the requirement of polymercompatibility, spinnings were made with dopes containing 25% of theacrylonitrile polymer of Example I and 2.5% PEG 20,000, 2.5% PEG 6,000and cellulose diacetate, all of which yield turbid inhomogeneoussolutions when blended with the acrylonitrile polymers. Void counts onthese fibers are given in Table III.

To study the eifects of additive level on void formation duringcoagulation, a series of fibers were spun incorporat- 03 ing varyinglevels of PEG 1,000 into a 25% solids solution of the polymer of ExampleI, and the resulting dopes spun under identical conditions. fibers aregiven in the following table.

While 0.5% additive gives an improvement in void count, optimum voidcontrol requires about 1.0% additive or more.

EXAMPLE V To study the effect of solids level on void formationspinnings were made using the polymer of Example I at 20 and 25% solidswith and Without 2.5% PEG 1,000 added. Results are presented in Table V.

Void counts on these suitable extrusion orifice to effect the formationof fibers and filaments therefrom.

2. Claim 1 wherein said polymer is polyacrylonitrile.

3. Claim 1 wherein said polymer is a copolymer com prising at least 85percent polyacrylonitrile and up to percent of a copolymerizablemono-olefinic monomer.

4. Claim 1 wherein said polymer is a blend of 80 to 99 percent of (A) acopolymer containing from 80 to 98 percent of acrylonitrile and 2 topercent of a copolymerizable mono-olefinic monomer and from 1 to 20percent of (B) a copolymer containing 10 to 70 percent of acrylonitrileand to 90 percent of a Vinyl substituted tertiary heterocyclic aminesaid blend having an overall vinyl substituted tertiary heterocyclicamine content of from 2 to 20 percent based on the weight of the blend.

5. Claim 1 wherein the solvent is N,N-dimethylacet amide. V

6. Claim 1 wherein the solvent is dimethylsulfoxide.

7. Claim 1 wherein the polyglycol is polyethylene glycol.

8. Claim 1 wherein the polyglycol is polypropylene glycol.

Table V No. of TR Cycle to break Solids Additive voids/10 Den. Ten.Elong.

level micron length Dry Wet Dry Wet I 20? N011 25+ (Fiber too poor fortextiie evaluation) 20% PEG 1,000 2 3.1 2. 0 43 1. 0 1. 7 1, 138 835 25None 6 3.2 2.0 '34 1.3 3.0 754 422 25" PEG 1,000 0.1 3. 1 2. 2 32 0.30.5 800 525 EXAMPLE VI 9. Claim 1 wherein the molecular weight of thepoly- To establish the lower limits additive of molecular weight usefulin the practice of this invention, spinnings were made using a series ofhomologous materials beginning with ethylene glycol and working upward.Polymer used was the polymer of Example I at 25 solids and spinningswere conducted under identical conditions with each additive. additiveon void formation.

These results show that while addition of even the lowest molecularweight number of the series gives some control over void formationoptimum control is achieved only at molecular weights above 200.

Substantially void free fibers and filaments are also obtained whenpolypropylene or polybutylene glycols of suitable molecular weight areemployed.

As many variations of this invention may be made without departing fromthe spirit and scope'thereof it is to be understood that the inventionis not limited to the specific embodiments thereof except as defined inthe appended claims.

We claim:

1. A process for the production of void free fibers and filaments fromacrylonitrile polymers comprising mixing an acrylonitrile polymercomprising at least 85 percent acrylonitrile, an organic solventtherefor, and from about 1 to about 25 percent based on the weight ofthe polymer of a polyglycol of from 1 to 4 carbon atoms and having anaverage molecular weight of from 400 to 4,000, stirring and thereafterextruding the resultant polyglycol polymer spinning solution through aTable VI shows the results of each glycol is from 400 to 2,000.

10. Claim 1 wherein the polyglycol is polyethylene glycol of 400molecular Weight.

11. Claim 1 wherein the polyglycol is polyethylene glycol of 1,000molecular weight.

12. Claim 1 wherein the polyglycol is polyethylene glycol of 4,000molecular Weight.

13. A process for the production of void free fibers and filaments fromacrylonitrile polymers comprising mixing 25 percent by weight of anacrylonitrile polymer comprising 93.7 percent acrylonitrile and 6.3percent vinyl acetate, percent by weight of N,N- dimethylacetamide and2.5 percent by weight of polyethylene glycol of 1,000 molecular weight,stirring and extruding the resultant polyethylene glycol polymerspinning solution through a suitable extrusion orifice to effect theformation of fibers and filaments therefrom.

References Cited by the Examiner UNITED STATES PATENTS 2,517,694 8/50Merion et al. 28-82 2,715,763 8/55 Marley 28-82 2,752,317 6/56 Sudekum260--29.1 2,801,982 8/57 Fuchs 260--29.1 2,878,226 3/59 Jenkins 26032.62,904,391 9/59 Bennett et al. 1854 2,916,348 12/59 Cresswell l854FOREIGN PATENTS 1,085,645 7/60 Germany.

References Cited by the Applicant UNITED STATES PATENTS 3,080,210 3/ 63Ucci. 3,088,188 5/63 Knudsen. 3,088,793 5/63 Knudsen et a1. 3,124,629 3/64 Knudsen.

ALEXANDER H. BRODMERKEL, Primary Examiner.

WILLIAM J. STEPHENSON, MORRIS LIEBMAN,

- Examiners.

1. A PROCESS FOR THE PRODUCTION OF VOID FREE FIBERS AND FILAMENTS FROMACRYLONITRILE POLYMERS COMPRISING MIXING AN ACRYLONITRILE POLYMERCOMPRISING AT LEAST 85 PERCENT ACRYLONITRILE, AN ORGANIC SOLVENTTHEREFOR, AND FROM ABOUT 1 TO ABOUT 25 PERCENT BASED ON THE WEIGHT OFTHE POLYMER OF A POLYGLYCOL OF FROM 1 TO 4 CARBON ATOMS AND HAVING ANAVERGE MOLECULAR WEIGHT OF FROM 400 TO 4,000, STIRRING AND THEREAFTEREXTRUDING THE RESULTANT POLYGLYCOL POLYMER SPINNING SOLUTION THROUGH ASUITABLE EXTRUSION ORIFICE TO EFFECT THE FORMATION OF FIBERS ANDFILAMENTS THEREFROM.